Most of known carborne antennas are pole-type antennas (whip antennas) which project from their car bodies.
In some cars, a so-called glass antenna in the form of a wire embedded in a window glass is used. It is further proposed to receive signals by detecting a high-frequency current induced in the roof, etc. of a car body, using a pick-up coil.
Some pole-type antennas are stationary in a projecting configuration, and some of them can be extended and contracted by a user. In both designs, there is a great possibility that they are snapped off or bent accidentally and lose their signal receiving function. Further, different mounting arrangements including most suitable water-proof mechanisms are required for different car models. Besides, since each such antenna is designed to be optimum under a specific band, some antennas for different specific reception bands must be mounted on a car for acceptable wide-band reception. These factors apparently damage a good appearance of a car (in particular, passenger car, etc.). A glass antenna is one of the alternatives which does not project to the exterior of the car and maintains the good appearance of the car. However, considering that the reception band is broadened in these days, such a glass antenna does not have a sufficient capacity, and a user is forced to use it in addition to one or more pole-type antennas.
The above-introduced arrangement configured to pick up a high-frequency current induced in the roof, etc. of a car is in the form of a relatively small-scaled magnetic member (ferrite core) which is wound with a coil. This appears to be operative in strong electric field areas. However, in weak electric field areas where the current induced in the car body is small, the detected amount is too small to obtain an acceptable receiving sensitivity because a booster, if used for amplifying the small detection amount, also picks up engine noises, etc.
Besides this, when a member thereof operative as an antenna element is positioned close to a conductive member such as a car body, changes occur in electrical characteristics of the antenna. Therefore, it must be isolated from other conductive members as in the case of pole-type antennas. This is because an antenna equivalent circuit is in the form of a distributed constant circuit of L, C and R as is known in general, and it loses a stable antenna function because of changes in L, C and R when any other conductor (metal member including a car body) is near the antenna. Therefore, when it is used as a carborne antenna, its function is affected by its mounting condition.